This invention relates to a rotational polygon mirror used in the optical apparatus or the like of a laser scanning system and to a method of manufacturing the same.
A rotational polygon mirror is mounted on the optical apparatus or the like of a laser scanning system and is used to change, for example, the course of the laser beam and cause the laser beam to scan on a light-receiving surface and typically, a rotational polygon mirror of a structure in which the side surface of a polygonal member whose cross-sectional comprises a regular polygon such as a regular hexagon is formed as a reflecting mirror surface is known.
Such a rotational polygon mirror has heretofore been manufactured by a method comprising shaping an optical glass member into a regular polygonal shape by a step such as grinding or polishing, and further polishing the side surface of the polygonal pole to thereby form a reflecting mirror surface, or a method comprising cutting and shaping a member formed by a metal material such as an aluminum alloy into the form of a polygonal pole whose cross-section is of a regular polygonal shape, and super-precision-cutting the side surface thereof by the use of diamond cutting tool to thereby form a reflecting mirror surface.
However, in the manufacture of the rotational polygon mirror by the above-described methods, the shaping of a polygonal pole-like base member by the cutting or the like or an optical glass or metal material member and the formation of a reflecting mirror surface of good accuracy by polishing or cutting have required much labor and time and a high-degree technique and particularly, the formation of the other portion than the reflecting mirror surface into a complicated shape has required a more complicated and higher-degree step, which in turn has led to a problem of higher cost of manufacture.
Also, the use of optical glass or a metal material as the base member has led to the heavy weight of the rotational polygon mirror itself, and this has been a hindrance in reducing the weight of the apparatus to which the laser rotational polygon mirror is to be mounted.
It is an object of the present invention to provide a rotational polygon mirror which can be simply formed at a low cost of manufacture and a method of manufacturing the same.
It is another object of the present invention to provide a rotational polygon mirror which is light in weight and which can be simply formed at a low cost of manufacture and a method of manufacturing the same.
It is still another object of the present invention to provide a method which can simply form even a rotational polygon mirror in which the other portion than a reflecting mirror surface is complicated, at a low cost of manufacture.
The above objects of the present invention are achieved by the following rotational polygon mirror and the following method of manufacturing the same.
That is, the present invention is a rotational polygon mirror having a polygonal pole-like portion on one or more of whose side surfaces a reflecting mirror surface is provided, characterized by a base member having a polygonal pole-like portion formed of a light-weight material which can be easily molded into a complicated shape, such as resin, a composite resin material comprising chiefly resin, aluminum or an aluminum alloy, a coating film which is provided on one or more side surfaces of the polygonal pole-like portion and on which the reflecting mirror surface is formed, and a coating film functioning as a reflection increasing film and/or a protective film provided on the reflecting mirror surface as desired, and a method of manufacturing the rotational polygon mirror which comprises the steps of forming a base member having a polygonal pole-like portion from said material, forming a coating film of single-layer or multi-layer structure on a portion of said base member on which at least the reflecting mirror surface is formed, forming at least the portion of said coating film which forms the reflecting mirror surface into a reflecting mirror surface as desired in a case where, in the step of forming said coating film, the portion on which the reflecting mirror surface is formed does not yet have sufficiently the accuracy necessary for the reflecting mirror surface, and providing a coating film functioning as a reflection increasing film and/or a protective film on said reflecting mirror surface as desired.